Text as watermark looks unsharp

The text I've created in GIMP, with transparent background, (200 x 29) added as a watermark.png to a web video php script, displays ok on the uploaded video, overlayed as a watermark, on the smaller screen (Screen-small1.png - attached example), but still not really sharp looking, and definitely unsharp/jagged when full screen is selected (Screen-large.png -attached example).